Location-Based Services (LBS) have a growing relevance to marketing, social networking, health, business and security applications. LBS can be used to direct customers in a shopping centre to find a certain store, monitor the movements of patients in a hospital, track a package in a shipping facility, monitor the security of a building by evaluating the density of guards using WiFi® devices, or trigger an alarm when a person enters a restricted area.
Global Positioning Systems (GPS) is a widely-used and cost-effective positioning technique, but it is not available or suitable for all environments. Obstacles such as walls, ceilings tunnels and the like render GPS ineffective, and high-rise urban buildings are known to affect positioning accuracy.
Other techniques used to implement LBS include RFID and Infrared technology which exhibit limitations similar to GPS LBS. For instance, Non-Line-Of-Sight (NLOS) environments can affect the LBS performance and the above techniques and technologies typically require dedicated hardware, software and infrastructure.
WiFi® (IEEE 802.11) is a wireless network signalling technique, which can also be used for LBS and is very widely distributed in both indoor and outdoor environments. WiFi Positioning Systems (WPS) have many advantages over the above techniques and technologies in terms of accuracy, coverage and cost-effectiveness. WPS use the same equipment which establishes wireless networks, and which is configured as a positioning system without requiring additional hardware and/or firmware or network setting modifications. As a result, WPS has become an attractive proposition for LBS in both indoor and outdoor environments. Current WPS techniques rely on either geometric or non-geometric methods. In the case of a geometric method, all network Access Points (APs) involved in the calculations need to be part of the same network to which the Mobile Unit (MU) is connected, since the method relies upon data packet communications and their acknowledgement between the APs and the MU. On the contrary, in the case of a non-geometric method, not all network Access Points (APs) involved in the calculations need to be part of the same network to which the Mobile Unit (MU) is connected, and the method indeed allows use of a substantially adjacent AP that is part of a different network.
Geometric methods include triangulation, which relies upon the Angle of Arrival (AoA), and multilateration, which relies upon the Time of Arrival (ToA) or the Time Difference of Arrival (TDoA). These geometric methods suffer from low accuracy of positioning, compared to non-geometric methods, particularly in Non-Line-Of-Sight (NLOS) environments. Non-geometric methods rely upon one or more Received Signal Strength Indicators (RSSIs) and such non-geometric methods include Cell location based on Cell Identifiers (Cell ID), Fingerprinting and trilateration. The accuracy of the Cell location method is depends on the density of Access Points (APs) or cell density. Fingerprinting and trilateration are generally more accurate than the Cell location method and although fingerprinting is dynamic (and can be used in any environment), it is not ubiquitous. In contrast, trilateration is ubiquitous but not dynamic.